1898] COLOURING MATTERS OF FLOWERS 199 



aldehydes, and HCl produced in every case a crimson resinous matter 

 which was not turned green by alkalies and acetate of lead. This 

 green reaction is however yielded by a substance which is obtained 

 by heating the lead or zinc compound of the pure tannin of the 

 horse-chestnut, etc., with dilute HCl, filtering off the phlobaphene 

 and shaking the red filtrate with amyl alcohol, which dissolves a red 

 substance which is washed with cold water and dissolved in ethyl 

 alcohol. This seems to be the most successful attempt that has yet 

 been made in the way of producing by synthesis the anthocyan and 

 erythrophyll of flowers and leaves ; and there seems little doubt that 

 some such process as this is brought about in nature by the con- 

 centration of the cell sap through increased transpiration, etc., from 

 these organs. It is as well to mention that, according to Jodin, 

 light does not exert a photo-chemical action on tannin, although it 

 does so on chlorophyll and carotin. Also that MM. Gautier and 

 Girard experimenting on the regulated oxidation of the tannins 

 came to the conclusion in 1877 that the red colouring matter of, e.g., 

 wine is only one of the transitory oxidation products of the oeno- 

 tannin contained either in the skin or pulp of the grape. Tschirch 

 likewise has pointed out that in the cell sap the tannins are oxidised 

 directly (or, if they are glucosides, after resolution into their con- 

 stituents) to red-brown phlobaphenes, some of which are formed very 

 slowly, while others are formed very rapidly. 



The latter class, viz., the protocatecliuic acid-tannins, may be 

 regarded as chromogens which evolve colouring matters not out of 

 their own molecules by condensation and dehydration, but possess 

 the property of forming coloured salts which turn blue, red, or even 

 green when exposed to the air. It is possible, indeed, that they 

 contain a salifiable group (chromophor) in their chemical structure ; 

 they are more entitled to be called tannic acids than the aforesaid 

 class are. Their most important peculiarity, however, patent to 

 everybody, is that they can embody a true blue flower. No one 

 has ever seen, or ever shall see, a blue rose ; Imt a blue dahlia or 

 even a blue daisy is quite possible. The very fact of this possi- 

 bility emanating, so to speak, from a source which is distinctly acid 

 argues a power of fixation which is something stronger than that 

 shown on the formation of a mere ' lake.' It was astutely observed 

 by Stein that decidedly blue flowers, such as corn-flowers, contain a 

 large quantity of calcium, phosphoric acid, and pectin. From ex- 

 periments which I have recently made, I am much disposed to con- 

 clude that the presence of a certain kind of pectin associated with 

 certain inorganic bodies explains the production of blue from the 

 tannic chromogen, and likewise the fact that even in an acid 

 medium the combination between these bodies is so complete that 

 no separation or reddening occurs. P. Q. Keegan. 



